Indeed, it's GLaDOS. That's really what makes the song for me. It's touching and frightening at the same time.

People who have played Portal 2 may not know this about the so-called Turret Opera, because it's not sung in English, but the lyrics are very meaningful and reveal an important element of the story. I won't say anything here, because spoilers, but for those who are done with Portal 2, it's well worth looking up a translation + explanation.

You can if you edit the .p8 externally, though everything's inverted - capitals will print in lowercase. Just don't save the .p8 in pico-8 afterwards, or it'll revert everything to lowercase again. exporting html/pngs will (should?) keep those changes though.

It actually is using the default font. It's just converting all characters to their smallcaps version before calling print(). You can see this in the innermost loop at the bottom of the source code. It's a clever way to fit more text vertically.

Great Work! Portal is one of my most favorite games and one of the greatest games of all time! (Has it really been over 10 years?!) and Portal 2 was amazing as well. I can almost hear GLaDOS's voice in my head while listening to this. Please do "Want you gone" next! some of the instrumental effects might be hard to do in pico-8(e.g. That part at the very beginning) but I'm sure you could make something close :)